Such a grid structure in the form of a grid fabric is disclosed by U.S. Pat. No. 2,115,667.
This grid fabric is used for the laminar reinforcement of road pavement. For this purpose, the grid fabric is laid on the foundation and covered with a bituminous asphalt coat. The grid consists of belts of fiberglass material and is therefore relatively rigid flexurally.
The road surface is then to be applied to the foundation prepared in this way, for example in the form of a coarse layer and a fine layer.
For the inlaid grid fabric not to be a hindrance when applying the road surface, it has to be held fast in the bituminous asphalt coat.
However, there are a number of parameters in this that can be optimally observed only with difficulty.
If the temperature of the asphalt coat is too high with appropriate thickness of the coat, there is a risk that the grid will sink in. The prestress inherent in the glass fibers can also lead to local lifting of the grid fabric out of the asphalt bed. If the temperature of the bituminous asphalt coat is too low, the grid floats. It may also happen that the retaining force of the asphalt coat on the grid fabric is too low.
In this case there is also a risk that the grid fabric will protrude from the asphalt bed.
To prevent this, it is also disclosed by DE 195 43 991 how to combine an appropriate grid fabric with a nonwoven fabric. This forms a grid fabric whose openings are filled fully with this nonwoven material.
This can indeed substantially increase the retaining forces of the bituminous asphalt coat on the grid fabric.
The penetration of the asphalt coat through the nonwoven layer, however, is very strongly dependent on time and temperature. For this reason there is a risk of the formation of cavities between the asphalt coat and the road surface.
This can be avoided only by another operating step, by applying an additional asphalt coat on the laid fabric-nonwoven fabric composite. This type of full-area composite also provides the capability of a water runoff barrier, which is advantageous in case of cracks in the road surface.
During the changeover from freezing to thawing periods, the penetration of water into the road foundation is substantially hindered. The water consequently runs off only to the side.
It is the purpose of this invention to provide a grid structure that keeps adhering until the road surface is applied, while avoiding additional operating steps and excluding defects in the asphalt coat.
The invention provides the benefit of a superproportional increasing of the retaining forces for the asphalt coat without loss of tensile strength of the interlaced strands of textile material.
This benefit is achieved by the fact that the invention integrates the basic concepts of the laminar bonding zone into the requirement of good penetration of the asphalt coat.
Because of the xe2x80x9conlyxe2x80x9d partially permeable filling of the grid fabric, enough open places remain in the individual grid openings through which the liquid bituminous asphalt coat can penetrate from the bottom of the grid structure to the top of the grid structure.
The grid structure pursuant to the invention is thus enclosed form both sides by a previously applied layer of bituminous material immediately after being laid down, so that on the one hand the problems of inadequate penetration are avoided, and at the same time the retaining forces on the grid structure are increased considerably.
The thin textile materialxe2x80x94from a microscopic viewpointxe2x80x94forms individual material fibers that can be retained in the asphalt coat, so to speak, and in this way can provide for a practically laminar composite by intercalation into the asphalt coat.
The thin textile material should be of an absorbent nature and the grid openings should fill up leaving open points of passage somewhat uniformly distributed.
Materials that are rough, fibrous, interlacing, and interleaving are advantageous.
Therefore, special importance is ascribed to the interleaving effect.
Each of the many individual fibers of the textile material is inlaid in the asphalt coating by itself, and is bound on practically on all sides. Since there is an intimate bond between the strands of the grid structure and the longitudinal-laminar belts, which partly fill up the grid openings, the retaining forces produced in this way are transferred to their full extent to the strength components of the grid structure. The strength components of the grid structure are the individual strands that are gripped between the grid openings.
The starting material for the longitudinal-laminar belts can be twisted and untwisted threads, fiber and/or staple fiber rovings.
The thickness of the longitudinal laminar belts should not exceed the thickness of the strands of the grid if possible.
In this way, the grid structure is reliably prevented from floating even with a relatively thin asphalt coat.
To facilitate the penetration of the asphalt coat at the passage holes, the thickness of the belts should decrease slightly toward the edges of the belts.
In addition, the so-called capillary effect can also be utilized in this way, since the fiber thickness at the edges can be somewhat less than in the center of the laminar belt.
The microscopic cavity areas formed in this way at the edges favor the penetration of the asphalt coat.
If the edges of the belts are unraveled essentially irregularly, a statistically favorable distribution of retaining forces is produced inside the grid openings.
If the edges of adjacent belts then merge into one another/are connected to one another with mutual contact, the belts in addition also contribute to the stabilization of the grid structure and nevertheless permit the xe2x80x9cfloodingxe2x80x9d of the reinforcing material with the asphalt material.
It is immaterial in principle whether the longitudinal-laminar belts run in the warp direction or in the woof direction of the grid structure of the grid fabric. When the belts run in the woof direction, the belts can also connect to the warp threads of each strand, e.g., they can be knitted, glass fiber/rovings composites, or interwoven. This leads to a lattice structure with stable design and high strength without impairing the strength of the individual strands. This also applies to belts that run in the warp direction.
An embodiment in which the laminar fraction of the belts amounts to more than 50% based on the area of the grid opening is advantageous.
Degrees of filling of about 10-90% meet the requirements of the invention.
The belts can be formed from thin parallel threads, thin ribbons, or a thin roving of fibers/staple fibers.
It is desirable according to the invention for the grid structure to be applied onto a polymer bitumen dispersion. This should have a softening point of about 90 degrees Celsius.
If this is a plastic with a polymer bitumen fraction, an intimate bond is produced between the coating and the bituminous asphalt coat on the road foundation from fusing together.
The polymer bitumen fraction supplies the ability to heat-seal the polymer bitumen dispersion and is practically equivalent to a two-part composite between the road substructure and the grid structure.
Suitable materials for the warp, woof, and belts are glass and polyester, as well as any other materials suitable for reinforcing grids.
Since the fractions of glass and polyester, for example, can each be between 0 and 100% by weight, it is recommended that the fractions of glass in each case be supplemented by the fraction by weight of polyester to make 100%.